Large quantities of blood from slaughterhouses are sent to working-up plants, where the blood is processed into dried blood products which are primarily used in fodder mixtures for livestock, or where it is fractionated to recover the blood plasma for use in all kinds of food products. The major part of the valuable protein content, present in the hemoglobin fraction of whole blood, is however currently used mainly as an animal feed additive since minor amounts of hemoglobin impart an undesirable dark colour and an unpleasant odour and taste to food products. Other factors that limit the use of blood products in food or even as a additive to animal feed are their high iron contents and their insufficient functional properties.
Over the years, various attempts have been made to remove the iron from whole blood and blood fractions, in particular from the hemoglobin fraction, and to decolourize the product.
Danish Patent Application No. 5508/86 discloses a process for producing decolourized hemoglobin by mechanical opening of the blood cells, adjusting the pH to 1 of 2 by means of an acid and adding 1 to 5% by weight / volume of an oxidising agent, in particular hydrogen peroxide, in the presence of carbohydrate derivative containing dienol groups, such as ascorbic acid. After oxidation, side products such as cell debris and heme-groups are removed and the decolourized protein fraction is recovered.
In European Patent Application No. 148 114, a process for producing decolourized hemoglobin is disclosed that encompasses treating whole blood in the presence of a proteolytic enzyme at a pH of 3.5 to 4 to denature the globin chains and thus render the heme-group more accessible to the action of an oxidising agent.
U.S. Pat. No. 4,180,592 discloses decolorization of blood by treating blood with an excess, e.g. 3 to 6% by weight, of an oxidising agent such as hydrogen peroxide after which excess hydrogen peroxide is removed by adding a further amount of blood.
The currently known methods apparently aim at separating the heme-group from the globin fraction either starting from whole blood or from the hemoglobin fraction.
These known methods aim at reducing the taste, odour an colour drawbacks of the resulting protein products by substantially removing the iron / heme fraction from the product. These methods however are still unsatisfactory either in that they require large amounts of oxidising agents, which affects the production costs as well as the properties of the protein products due to the oxidative action on sulfur containing amino acids such as Cystin, Cystein, Histidin and Methionin, and/or require rather expensive process adjuvents to avoid the latter drawbacks, in that they yield protein products having properties which are still not optimal in respect of taste, odour and colour or in that they yield protein products having low functionalities.
A totally different approach to processed hemoglobin products is known from EP 0 460 219. This patent discloses processed hemoglobin having an iron content of not less than 2 mg per g of solid content resulting from treating washed hemoglobin under alkaline conditions and treating the resulting product under oxidizing conditions.
However, a very important drawback of globin protein products known in the art is that they all have an isoelectric point in the range of 6-7, which isoelectric point corresponds to the isoelectric point of the hemoglobin.
This fact considerably affects the application possibilities in food products of the currently available blood protein and globin protein products. The solubility of proteins is indeed very low at their isoelectric point and food products usually have a pH value ranging from 5 to 9. In particular processed meat products have a pH value ranging from 5.5-7.0.
The purpose of the present invention is to provide a new globin protein product having properties and characteristics unknown before in the art, in particular a bland, colorless protein product with a solubility pattern, emulsifying capacity, emulsion stability and waterbinding properties similar to those of caseinates, in particular to those of the so called "high viscous type" caseinates, and to those of other functional proteins such as soy isolates.